The invention is concerned with a glazing comprising filaments, for example an automotive glazing comprising heating filaments.
It is well known that parallel straight heater wires integrated into a glazing and viewed in transmission against a bright light source can produce obtrusive light diffraction patterns, particularly obvious in night time viewing conditions. Such diffraction patterns, also known as ‘starburst’, ‘sparkle’ or ‘star filter’ effect, comprise rays emanating from a point light source.
US20070187383 (Southwall) discloses that if a driver's eyes are focused into the far distance and heating wires stretched between the top and bottom of a windshield, then a ‘star filter’ pattern will be observed to the sides of any light source, causing distraction. A wire shape is disclosed, formed of a succession of quarter arcs, wherein no portion is linear.
US20100200286 (Saint Gobain) discloses a conductive grid structure for minimising the optical impact of diffraction patterns. The structure is applied by a deposition and removal process, preferably optical lithography.
EP2284134, EP2381739 and EP2555584 (L G Chem) disclose many interconnecting conductive lines between nodes aimed at minimizing diffraction and interference of light. Irregular patterns of many interconnecting lines are disclosed which provide uniform heating per unit area. A disadvantage of many interconnecting lines for heating is that not all conductive lines carry equal current. Vision may be unnecessarily blocked by conductive lines which are electrically redundant.
EP2286992 and EP2278850 (Fujifilm) disclose wires formed into wavy lines and arranged in a mesh. A number of periods of the waves occur between intersections with the aim to reduce deterioration of a displayed image due to interference of diffracted light.
There remains a need for an alternative glazing comprising filaments for heating, which further minimises a starburst effect.